Chemical processes present challenges for traditional control strategies, in that many involve nonlinearities, time delays, and unknown process parameters. Robust control has emerged as a means to design control systems that can handle these complexities. Unlike conventional control design, robust control accounts for uncertainties in the models used to design the controller. Accounting for these uncertainties enables the design of a control system that maintains stability and achieves the specified performance under all operating conditions. Robust control design is gaining in popularity and has evolved to the point where fairly automated procedures exist now for use by practicing engineers.
This article discusses robust PID control design, emphasizing its usefulness for the chemical process industries. It points out the limitations of conventional control design and illustrates the usefulness of robust control by providing two examples, one involving a first-principles model and the other making use of a model based on experimental data. Finally, the article identifies limitations of linear controllers and offers potential solutions.